What Is Triploidy?

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What Is Triploidy?

Triploidy, or triploid syndrome, is a chromosome abnormality that occurs when there is an extra set of chromosomes present. Human beings are each supposed to have 46 chromosomes (23 pairs). A person gets half of each pair of chromosomes from each parent. Triploidy means that a baby has three sets of the 23 chromosomes rather than two, making a total of 69 chromosomes.

Unfortunately, triploidy is a disorder that is incompatible with life. The majority of fetuses that have triploidy die before birth and those that make it to term rarely survive the first months of life.Many times, babies that make it past 24 weeks gestation, die in the womb and are stillborn.

Most cases of triploidy involve "full" triploidy, meaning all the body's cells are uniformly affected. In rare cases, the triploidy can be "mosaic," meaning some of the body's cells have three copies of each chromosome and others have a normal set of 46 chromosomes.

There is some evidence that individuals that have mosaic triploidy may be less severely affected by the disorder than those with full triploidy. But even with mosaic triploidy, the prognosis is not good.

Some pregnancies affected by triploidy will also be affected by a partial hydatidiform mole (partial molar pregnancy), meaning there is an abnormal placenta that can, in rare cases, cause life-threatening complications for the mother. However, not every case of triploidy will be a molar pregnancy.

Symptoms

When a person is pregnant with a triploidy fetus, they may experience high blood pressure and swelling. They also excrete albumin in the urine (albuminuria), which can result in a condition called toxemia or preeclampsia. Additionally, the placenta is usually large, immature, and filled with cysts.

Meanwhile, a triploidy fetus usually has heart defects, abnormal brain development, adrenal and kidney defects, and spinal cord malformations. They also tend to have abnormal facial features such a widely-spaced eyes, low nasal bridge, low-set malformed ears, small jaw, and a cleft lip and palate.

The third and fourth fingers and the second and third toes of a triploidy fetus may be united and there may be deformity in the fingers and toes. Additionally, triploidy can cause liver and gallbladder issues as well as twisted intestines.

Those with mosaic triploidy may survive longer than those with full triploidy, but they will experience a number of complications. These include seizures, intellectual disabilities, and developmental delays. They also may have short stature, obesity, and other abnormalities.

Causes

Triploidy, which affects 1 to 3% of all pregnancies, can be caused by two different forms of abnormal fertilization. These include:

  • Diandric fertilization: This fertilization occurs when two sperm fertilize a single egg or when an egg is fertilized by a sperm that has an extra set of chromosomes.
  • Digynic fertilization: This type of fertilization occurs when a normal sperm fertilizes an egg that has multiple chromosomes.

Two-thirds of all triploid pregnancies are male fetuses. Meanwhile, occurrence of triploidy is not caused by maternal or paternal age.

Diagnosis

Sometimes the first indication of triploidy is major malformations, restricted growth, and low amniotic fluid during an ultrasound. Triploidy can be diagnosed through amniocentesis or blood testing of a newborn baby, known as karyotyping, or from tissue from a pregnancy loss.

Screening tests such as ultrasound and alpha-fetoprotein testing may show warning signs of triploidy. But these tests cannot confirm a diagnosis of triploidy.

Abnormal hCG levels can be found in some pregnancies with triploidy, and an ultrasound can show the characteristic placenta associated with a partial molar pregnancy.

Prognosis

Sadly, triploidy is a fatal condition with no cure or treatment for the condition. As mentioned above, almost all (more than 99%) of babies with triploidy are miscarried or stillborn. Of those born alive, most die in the hours or days following birth.

A handful of babies with triploidy have lived a few days or months after birth, with the longest known survivor living 10 1/2 months. But these reports are rare, and usually, the babies who survive longer have mosaic triploidy, rather than full triploidy. Affected babies usually have multiple birth defects and severe growth restriction.

Treatment

If your baby has been diagnosed with triploidy via amniocentesis, which is usually performed between week 15 and week 20 of pregnancy, you will probably be asked whether you wish to continue the pregnancy.

This decision is an individual choice and you have to decide what works for you. Some people prefer to terminate pregnancies that have fatal diagnoses, whereas others choose to continue the pregnancies, even though they are aware of the expected outcome.

In some cases, a pregnancy may be affected by a partial hydatidiform mole. In these situations, there is no chance of the baby making it to term and being born alive. Your doctor likely will recommend termination to prevent possible serious complications that could affect your health.

Unfortunately, there is a lot of confusing information about triploidy out there, so if your baby has been diagnosed with this condition during pregnancy or as a newborn, you are likely swimming with emotions, including numbness, confusion, and grief.

The first thing you need to know is that you didn't do anything to cause this to happen, and there is nothing that could have prevented it from happening. It is OK to grieve or to feel whatever else you may feel.

It may help to find a support group to help you process your feelings or emotions. Finding a counselor or therapist that specializes in pregnancy loss also can be helpful.

The key is that you not only take steps to heal from this experience, but that you also focus on self-care during this difficult time. With support, time, and patience you will be able to process what happened as well as learn strategies for coping with pregnancy loss.

The Risk of Recurrence

Researchers have not found any identifiable risk factors for having a pregnancy that's affected by triploidy. Even maternal age does not seem to be a risk factor.

A small number of people may have recurrent miscarriages affected by triploidy. But in the majority of cases, triploidy occurs randomly and is a one-time tragedy that does not repeat in future pregnancies.

If you have received a triploidy diagnosis following the testing of tissue from a miscarriage or stillbirth, the odds of it happening again are slim.

Triploidy vs. Trisomy

Both triploidy and trisomy are chromosomal abnormalities involving extra chromosomes. With trisomy, the fetus has an extra chromosome, meaning they have 47 chromosomes instead of 46.

Triploidy, on the hand, means that the fetus has three sets of chromosomes or 69 chromosomes. The human genome has 46 chromosomes or two sets of 23. With triploidy, the fetus has a third set.

Both triploidy and trisomy result in abnormalities that can be severe, but triploidy is not compatible with life whereas with some types of trisomy, like Down syndrome, the baby can live a long and healthy life.

Triploidy
  • Chromosome abnormality

  • Contains 69 chromosomes or 3 sets

  • Results in severe conditions not compatible with life

  • Types include full triploidy and mosaic triploidy

Trisomy
  • Chromosome abnormality

  • Contains 47 chromosomes or 1 extra

  • Leads to abnormalities that can be severe

  • Types include Down syndrome, Edwards syndrome, Patau syndrome, and mosaic trisomy

A Word From Verywell

If you've recently been diagnosed with a triploidy pregnancy, it's important that you find support as you come to terms with the news. There are numerous support groups for parents of babies with serious chromosomal disorders, and you may find these comforting as you process and cope with this condition.

If the triploidy diagnosis came after your baby was born, it's a good idea to speak with a genetic counselor about what you should expect in terms of caring for your baby. Most of the time, the recommended treatment is to provide comfort care rather than to pursue any intensive interventions.

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Article Sources
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